Protective cover for apertures for loud-speaking instruments, microphones, and otherarticles



April 11, 1944. D. H. MARLOW 23469226 PROTECTIVE COVER FOR APERTURES FOR LOUDSPEAKING INSTRUMENTS, MICROPHONES AND OTHER ARTICLES iled Dec f E Q 7 w Patented Apr. 11, 194-4 iisrrso stares EMT OFFICE Dennis Herbert Marlow, London, England, assignor to British Rota Limited, London, England, a

British company Application-December 11, 1942, Serial No. 468,694 in Great Britain September 16, 1941 7 Claims.

This invention consists in improvements in or relating to protective covers for acoustic instruments such for example as apertures for loudspeaking instruments, microphones and other sound producing or reproducing instruments and has for its object to provide a water tight cover therefor. In one application of the invention the cover is applied to th casing for a loudspeaking instrument or for a microphone to be utilised on marine vessels where itis essential that sounds shall be emitted from-or transmitted into an enclosing casing but that access of water to the interior of the casing shall be entirely prevented.

A Water-tight cover according to the presentinvention comprises in combination a yielding or other diaphragm constituting the cover proper, water-tight yielding marginal. retaining means for securing the diaphragm within or around the aperture, and a protective grid or grids secured over and spaced from one or from both faces of the diaphragm. In order that the invention may be more clearly understood two preferred forms Will now be described with the aid of the accompanying drawing, each of which represents in central section those parts of-the construction necessary to the understanding of the invention.

In the figure the invention is illustrated as applied to the casing of a loudspeaking. instrument of the type normally employed in marine vessels. In such instruments a loudspeaker iii of cone or of any other preferred type is enclosed in a metal casing II, a cylindrical upper portion of Which is illustrated in the drawing.-

This casing is open only in that wall which faces the interior of the cone or equivalent portion of any alternative loudspeaking device ex cept for means for entry of electrical leads necessary for the operation of the loudspeaker. The opening referred to is indicated at l2 and is provided in a readily removable cover or bezel 13 which is secured to the casing H in a Watertight manner. In the form shown bolts and nuts represented generally by the reference numeral M are fitted at spaced intervals around the peripheries of outwardly-extending register ing flanges on the casing l! and the cover i 3 so that the two parts can be bolted tightly together and a compressible packing washer #5, located in an annular groove in the cover 13, serves to effect a water-tight seal between the meeting faces of the flanged portions of the casing and cover.

Behind the aperture I2 access to the cone l0 (Cl. 16li330) isobstructed accordance with this invention by means of an oil-sill: diaphragm 16 which is'gripped around its margin between two moulded or other rubber rings 1''! and 18, one on each side of the diaphragm, and these rings are themselves firmly held between the inturned outer flange of the cover it and an opposed stationary ring fitted within the body of the casing to constitute, in the example illustrated, also a support for the margin of cone H3. The ring I9 is usually an integral part of the loudspeaker assembly.

Thus when the parts are assembled, the oililk diaphragm 56 in conjunction with the rings i? and. it provides a water-tight closure and the diaphragm itself will be sufliciently thin to allow for adequate emissionof sounds from the cone ill,

The diaphragm i6 is stretched tightly and during or prior to assembly will be secured in its stretched condition to either one or the other of rings ll or iii by means of any preferred adhesive, Whereafter the other ring will be applied to the opposite side of the diaphragm and the assembly of diaphragm and rings secured in the position. shown. Suchv a diaphragm by itself, whil v operating perfectly satisfactorily to prevent admission of water into that part of the casing containing the cone or other loudspeaking device, is relatively weak and. would not stand up for instance to blast caused by explosion. The present invention, therefore, further provides a comparatively fine mesh grid 2%] protecting the outer side of the oil-silk diaphragm with or without the provision of a second grid shown at, 2! to protect the. opposite face of the diaphragm. Preferably both grids 2i] and M will be provided and each of them will be slightly domed towards its centre so that it extends farther away from th diaphragm at the centre than it will nearer to the margin of the diaphragm. The edge of each grid is received in a radial slot formed in the appropriate rubber ring I'l, l8 and when the latter is or are compressed during assembly the margin of the grid or of each of them will be clamped firmly in position. The grid or grids will limit the degree to which the diaphragm can be distorted by the effect of blast or by other sudden applications of distorting forces which may reach the diaphragm. In other words, the rids such as 21) and 2! will restrict distortion of the diaphragm it to limits within which the latter can yield without rupturing. In order to give a greater yield to the margin of the diaphragm the opposed faces of the rubber rings are formed with annular channels 22, 23 situated at an intermediate position in the radial dimension of the rings so as to afiord a relatively thinner inner wall for each ring as compared with its maximum radial dimension. The diaphragm has been shown as extending completely across the full widths of the rings but it may be so made that its diameter is only sufiicient to stretch to the inner margins of slots 22, 23. This inner wall in each ring will flex to some extent to afiord a greater yield of the diaphragm as a Whole than would be the case if the rings were solid without the provision of slots such as 22 and 23.

In an alternative method of assembly the layer of silk I6 is first stretched to the desired extent over a temporary jig and then placed on to the surface of the rubber ring I 8 with adhesive interposed between them to secure the silk in position. Before thus sticking the silk on to the ring the inner annulus of ring I8 (i. e. that portionlocated inside channel 23) is forced slightly inwardly by temporarily inserting in the channel a rubber or other ring, the diameter of which is somewhat greater than the radial Width of the channel, When the silk is firmly attached to the inner portion only of ring [8 the ring is removed from channel 23, and the silk trimmed off, whereafter further assembly of the parts is completed as already explained.

By this means the tendency of the inner annulus of ring 23 is to return and thus maintain the silk in the required degree of tension.

In order to provide sufficient strength to the channelled rings the margins of the protective grids are, as illustrated, offset outwardly so that the channels in the rings l7 and I8 in which they are embedded are at a greater axial distance from the diaphragm than the distance of approach of each grid to the diaphragm at a position immediately inside the rings.

The grids may be made of metal or other preferred material such, for example, as moulded synthetic resinous compounds or other hard-setting mouldable materials.

, While the specific form of the invention has been described as comprising circular covers and diaphragms, it will be understood that they may beof any marginal form to suit the requirements for the purposes for which they are to be used. The channels in the rings such as I! and I8 or H! and H8 will then naturally conform to the shape of the outer margin.

In manufacturing the form of the invention above described in which the opposed faces of the rings are channelled to give a greater flexibility to the margin of the diaphragm, the latter can first be secured over the entire radial width of the ring to which it is first attached and can then be cut away over the channel so that the diaphragm proper only remains secured to that portion of the ring lying radially inside the channel.

I claim:

1. For an acoustic instrument having a casing provided with an aperture through which sound is to pass, a water-tight cover for that aperture comprising in combination an impervious flexible diaphragm constituting the cover proper, ret'aining means for securing the diaphragm within the margin of the aperture, said retaining means being yielding and forming a water-tight connection between the edge of the diaphragm and the margin of the aperture and a protective grid secured over and spaced from one at least of the faces of the diaphragm.

2. A water-tight cover for the purpose specified comprising in combination a rigid margin surrounding an aperture, an impervious diaphragm constituting the cover proper, retaining means for securing the diaphragm within the margin of the aperture, said retaining means being yielding and forming a water-tight connection between the edge of the diaphragm and the margin of the aperture and protective rids secured over and spaced from both faces of the diaphragm.

3. A water-tight cover according to claim 1 in which the diaphragm is secured between compressible resilient rings which constitute the water-tight yielding marginal retaining means and in which the edge of the protective grid is also received.

4. A Water-tight cover according to claim 2 in which the edge of the diaphragm is secured between compressible resilient rings constituting the water-tight yielding marginal retaining means and in which are also received the edges of both protective grids, one grid in each ring.

5. A water-tight cover according to claim 1 in which the diaphragm is secured between compressible resilient rings which constitute the water-tight yielding marginal retaining means and in which the edge of the protective grid is also received, said rings being formed with opposed annular channels at positions intermediate the inner and outer peripheries of the rings.

6. A water-tight cover according to claim 1 in which the diaphragm is secured between rubber rings which constitute the water-tight yielding marginal retaining means and in which the edge of the protective grid is also received.

7. A water-tight cover according to claim 1 in which the margin of the protective grid is radially offset outwardly and its edge is embedded in its associated ring at an axial distance from the diaphragm greater than its distance therefrom at a position immediately inside the ring.

DENNIS HERBERT MARLOW. 

